In accordance with an exemplary scenario, global navigation satellite systems (GNSS) may be broadly defined to include GPS, Galileo, GLONASS, Beidou, IRNSS, QZSS and other positioning technologies using signals from satellites, with or without augmentation from terrestrial sources. Information from GNSS may be used to compute a user's position information (e.g., a location, a speed, a direction of travel, etc.).
In one exemplary scenario, a GNSS receiver autonomously evaluates the integrity of the information it receives from different GNSS satellites by a process referred to as “receiver autonomous integrity monitoring” (RAIM). Evaluating the integrity of the information involves, for example, checking whether the information received from a GNSS satellite is relatively free of errors, such as those errors introduced on account of a multipath effect, and removing erroneous information from the computation implemented to determine the position information.
In an exemplary scenario, the information received from GNSS satellites may be affected by multipath effect, especially in areas such as urban canyons, wherein an “urban canyon” may be defined as an area characterized by narrow lanes with tall structures, such as man-made buildings, on both sides. The information sent by the GNSS satellites may bounce off of, or be reflected from, one or more surfaces before being received by the GNSS receiver. As a result of the multiple paths travelled or encountered by the information, an accuracy of the information to be utilized in the computation of the position information may be compromised.
For the detection of a multipath error in the received information, and the subsequent removal of such information, to be accomplished, the information has to be received from at least five or six GNSS satellites, respectively. In urban canyons, it may be difficult to receive information from such a high number of GNSS satellites, as the visibility of GNSS satellites may be quite low in such areas.